In refrigerators, such as a refrigerant air conditioner, a car air conditioner, etc., refrigerants, for example, a chlorofluorocarbon (CFC), etc., have hitherto been used. However, since the CFC refrigerant is a compound containing a chlorine atom that becomes a cause of environmental problems, the refrigerant is being switched into a chlorine atom-free fluorinated hydrocarbon refrigerant, such as a hydrofluorocarbon (HFC), etc. As the HFC refrigerant, R32 (difluoroethane) and R134a (1,1,2,2-tetrafluoroethane), and furthermore, R410A (a mixture of difluoroethane and pentafluoroethane), which is a mixed refrigerant, and so on are used.
The refrigerators have a structure in which a mixture of a refrigerant and a refrigerator oil (hereinafter, the mixture is also referred to as “refrigerator oil composition”) is circulated within a closed system, and therefore, compatibility with the refrigerant, stability and lubricating performance are required for the refrigerator oil. In order to easily satisfy these requirements, refrigerator oils containing, as a major component, an oxygen-containing organic compound, such as a vinyl ether compound, a polyoxyalkylene glycol, etc., are generally used with the HFC refrigerant (see, for example, PTL 1).
In addition, in order to more improve the stability and lubricating performance of the refrigerator oil, it is known to add various additives to the refrigerator oil containing, as a major component, the oxygen-containing organic compound. For example, PTL 2 discloses that a phosphorus-based compound, such as tricresyl phosphate (TCP), etc., is added to a polyoxyalkylene glycol-based refrigerator oil.